A conventional electrophotographic color printer has a photoreceptor drum or belt, charging units, exposure units, and developing units each with a different color toner disposed in relation to the photoreceptor drum or belt. In general, a region of the photoreceptor drum or belt receives a uniform charge from one of the charging units and then the charged region is exposed by one of the exposure units to form a charge pattern on the region (latent image) corresponding to a light image. To develop the latent image, the photoreceptor drum or belt then carries the latent image to one of the developing units where the latent image is exposed to an associated charged toner that adheres to charged portions of the latent image. If two or more color toners are required to develop the latent image, then the previous steps are repeated. Once the latent image is completely developed (all colors applied), the photoreceptor drum or belt transfers the developed latent image to paper or other substrate. Typically, the conventional electrophotographic color printer has a fuser unit that uses heat and pressure to affix or fuse the developed latent image to the substrate. The conventional electrophotographic color printer also has a cleaner unit that is disposed in relation to the photoreceptor drum or belt and is employed to remove excess toner that was not transferred to the paper as part of the developed latent image.
Typically, components of the conventional electrophotographic color printer, such as the photoreceptor drum or belt, the charging units, the exposure units, the developing units and the cleaner unit, are arranged such that the printer is inconveniently large in size. In an effort to reduce size, some conventional electrophotographic color printers arrange components such that heat generating components are located close to the photoreceptor drum or belt. This conventional arrangement subjects the photoreceptor drum or belt to undue heating, a problem that causes premature aging and substantial wear of the photoreceptor drum or belt.
In addition, conventional electrophotographic color printers, such as disclosed in Smith U.S. Pat. No. 5,313,259 and Maruyama U.S. Pat. No. 5,473,421, have a photoreceptor belt designed to travel an oblong or triangular path with charging units, exposure units and development units as well as a cleaning unit disposed along one or more external sides of the oblong or triangular path of the photoreceptor belt so as to reduce the overall size of the printer. But at least one of the development units is disposed in relation to the photoreceptor belt such that a portion of developed toner released from the one development unit to adhere to the latent image on the belt falls down due to gravity so as to contaminate a region of the belt other than where the latent image resides. Thus, the printing quality of the conventional electrophotographic color printer is reduced. In addition, the portion of developed toner may fall down on to another region of the belt where another latent image resides, causing the other latent image to be polluted or blurred. Furthermore, the portion of developed toner from the one development unit may also fall and contaminate the toner of another development unit that is disposed beneath the one development unit.
Moreover, to achieve a compact size, the cleaning unit in conventional electrophotographic color printers, such as disclosed in the Maruyama Patent, is disposed in relation to the photoreceptor belt such that a portion of excess toner removed from the photoreceptor belt by a blade of the cleaner unit falls due to gravity to a lower region of the belt (and not directly to a waste container for easy removal), which potentially leads to contamination of a next latent image to be developed if the portion of excess toner is not “swept from” the lower region of the belt by the cleaner unit.
In addition, the conventional electrophotographic color printer typically has a transfer unit that is disposed at a bottom lateral plane of the photoreceptor belt. During transfer of the developed latent image from the photoreceptor belt to a sheet of paper or other substrate, the fed sheet is closely contacted with the transfer unit and the bottom lateral plane of the photoreceptor belt of the conventional electrophotographic color printer. If the movement of the belt along the bottom lateral plane is not fully synchronized with the fed sheet, the transfer of the developed latent image to the fed sheet may be blurred, twisted or unsuccessful. Therefore the synchronization of the transfer unit and the fed sheet is another problem in conventional electrophotographic color printers.